Post on 31-Aug-2020
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Dealing with StressDealing with Stress
I. What is environmental stress?
II. Strategies for Dealing with Stress
III. Costs and Benefits
StressStress
•• StressStress is any condition that lowers the is any condition that lowers the performance or survival of an organism.performance or survival of an organism.
•• Most environmental factors are stressful if Most environmental factors are stressful if they are experienced in extremes.they are experienced in extremes.–– temperaturetemperature–– lightlight–– humidity/salinityhumidity/salinity–– pHpH
Dealing with StressDealing with Stress
•• Avoid stressful environmentsAvoid stressful environments
•• Adjust to stressful conditions Adjust to stressful conditions (acclimation or acclimatization) (acclimation or acclimatization)
•• Keep body conditions different Keep body conditions different from environmental conditionsfrom environmental conditions(regulation or homeostasis)(regulation or homeostasis)
Geographic Variation in Temperature
Huey & Stevenson (1979), Huey & Stevenson (1979), American ZoologistAmerican Zoologist
Per
form
ance
Temperature
Temperature as a StressorTemperature as a Stressor
AntarcticaAntarctica
Chaenocephalus aceratus
Life exists within a limited range of temperatures.Life exists within a limited range of temperatures.
Hochochka & Somero (2002), Hochochka & Somero (2002), Biochemical AdaptationBiochemical Adaptation
Per
form
ance
Temperature
Why is temperature stressful?Why is temperature stressful?
Molecules are too loose.
Molecules are too stiff.
Dealing with StressDealing with Stress
•• Avoid stressful environmentsAvoid stressful environments
•• Adjust to stressful conditions Adjust to stressful conditions (thermal acclimation) (thermal acclimation)
•• Keep body conditions different Keep body conditions different from environmental conditionsfrom environmental conditions(thermoregulation)(thermoregulation)
Molecules are like materials:Molecules are like materials:Some flex while other do notSome flex while other do not
Per
form
ance
Temperature
Organisms can acclimate to stress.Organisms can acclimate to stress.
Test Temperature (οC)
18 30
Num
ber o
f Cop
ulat
ions
0
1
2
3
4Acclimated at 18οCAcclimated at 30οC
Wilson and Johnston (2005),Wilson and Johnston (2005),In: In: Animals and EnvironmentsAnimals and Environments
Mosquito fish(Gambusia holbrooki)
Dealing with StressDealing with Stress
•• Avoid stressful environmentsAvoid stressful environments
•• Adjust to stressful conditions Adjust to stressful conditions (thermal acclimation) (thermal acclimation)
•• Keep body conditions different Keep body conditions different from environmental conditionsfrom environmental conditions(thermoregulation)(thermoregulation)
Geographic Variation in Temperature
Temperature varies greatly on a small scale.
M. W. Sears et al. (unpublished)
Mechanisms of Heat ExchangeOrganisms regulate heat exchange via behavior, morphology and physiology.
BEHAVIORBEHAVIOR
Organisms can moveOrganisms can movebetween sun and shade.between sun and shade.
sun
shade
MORPHOLOGYMORPHOLOGY
Color and posture influence heat exchange.Color and posture influence heat exchange.
Orienting the body away from Orienting the body away from the sun prevents overheating in the sun prevents overheating in plants and animals.plants and animals.
MORPHOLOGYMORPHOLOGY
Color and posture influence heat exchange.Color and posture influence heat exchange.
Collared lizards use dark bands Collared lizards use dark bands to absorb heat rapidly. Lizards to absorb heat rapidly. Lizards raised in colder environments raised in colder environments have more bands. have more bands. ((RandriamahazoRandriamahazo & Mori 2005)& Mori 2005)
PHYSIOLOGY
Blood flow can be used to gain or lose heat.
““ColdCold--bloodedblooded”” animals can animals can maintain a stable temperature.maintain a stable temperature.
Australian Lace MonitorAustralian Lace Monitor
Body Temperature (oC)10 14 18 22 26 30 34 38 42
Rel
ativ
e P
erfo
rman
ce (%
)
0
20
40
60
80
100sprint speedenduranceenergy assimilation
Angilletta et al. (2002),Angilletta et al. (2002),Journal of Thermal BiologyJournal of Thermal Biology
Body Temperature (oC)10 14 18 22 26 30 34 38 42
Rel
ativ
e P
erfo
rman
ce (%
)
0
20
40
60
80
100sprint speedenduranceenergy assimilation
Body tempsBody temps
Angilletta et al. (2002),Angilletta et al. (2002),Journal of Thermal BiologyJournal of Thermal Biology
EndothermyEndothermy
Endotherms increase metabolism at low temperatures.
Data for Pygmy Possumsfrom Bartholomew and Hudson (1962)
Met
abol
ic h
eat p
rodu
ctio
n
Insulation is needed for endothermy.
Dark regionis warmest.Tuna heat some parts
through endothermy.
Pythons use endothermy to heat their eggs.
Moths use endothermy to heat up before flight.
Endotherms often dump heat by evaporation.Endotherms often dump heat by evaporation.
Because water stores much heat, losing water to air Because water stores much heat, losing water to air removes heat from the body.removes heat from the body.
Mechanisms of ThermoregulationMechanisms of Thermoregulation
Decrease Heat LossDecrease Heat Loss::
-- constrict blood vesselsconstrict blood vessels-- raise pelageraise pelage-- reduce surface areareduce surface area-- increase blubberincrease blubber
Increase Heat ProductionIncrease Heat Production::
-- shivershiver-- voluntary activityvoluntary activity-- increase metabolismincrease metabolism
Increase Heat LossIncrease Heat Loss::
-- dilate blood vesselsdilate blood vessels-- sweatsweat-- pantpant
Decrease Heat ProductionDecrease Heat Production::
-- reduce activityreduce activity-- reduce metabolismreduce metabolism
EndothermsEndotherms:: most heat derived from metabolismmost heat derived from metabolism
EctothermsEctotherms:: most heat derived from environmentmost heat derived from environment
HomeothermsHomeotherms:: maintain a stable body temperaturemaintain a stable body temperature
PoikilothermsPoikilotherms:: let body temperature varylet body temperature vary
Poikilothermic ectothermPoikilothermic ectotherm-- plants, sessile terrestrial plants, sessile terrestrial organismsorganisms
Poikilothermic endothermPoikilothermic endotherm-- bats, bears, & other animals bats, bears, & other animals that undergo torpor or that undergo torpor or hibernationhibernation
Homeothermic ectothermHomeothermic ectotherm-- some reptiles and most fish some reptiles and most fish
Homeothermic endothermHomeothermic endotherm-- most mammals and birdsmost mammals and birds
Which strategy is best?Which strategy is best?
•• Depends on the costs of the strategy Depends on the costs of the strategy relative to its benefitsrelative to its benefits
•• Can you think of some costs of these Can you think of some costs of these strategies? strategies?
–– Thermal acclimationThermal acclimation–– ThermoregulationThermoregulation